This application is based upon and claims priority of Japanese Patent Application No. 2000-142867, filed on May 16, 2000, the contents being incorporated herein by reference.
1. Field of the Invention
The present invention relates to a method of forming a dielectric film, and in particular, to a method of forming a dielectric film for use in a capacitor and a semiconductor device.
2. Description of the Related Art
In fields of semiconductor devices, attention has been attracted to a ferrodielectric or ferroelectric film and high dielectric substances having a high dielectric constant or permittivity. This is because that, for example, use of high dielectric films in a dynamic random access memory (DRAM) results in miniaturization or minimization of capacitors for storing a required value of electric charge and hence advantageously increases the degree of integration. A non-volatile memory can be implemented using ferrodielectric films for capacitors of the DRAM. For such ferrodielectric films and the high dielectric substances, research and development have been conducted on materials such as lead zirconate titanate (PZT) and lead titanate (PTO). These substances have a common chemical formula of ABO3.
Although lead zirconate titanate (PZT) doped with lanthanum (La), niobium (Nb), calcium (Ca), or strontium (Sr) is also known as a ferrodielectric substance, these substances will be collectively called lead zirconate titanate (PZT).
A dielectric film formed using oxide including lead is generally formed on a substrate by, for example, sputtering, sol-gel process, or chemical vapor deposition (CVD) at a room temperature. The dielectric layer formed at a room temperature is amorphous in an ordinary situation and will include a mixture of oxide of the constituent element. The film is then annealed at a temperature from 500xc2x0 C. to 800xc2x0 C. As a result, the film is crystallized to a target dielectric film.
To increase the integration degree of the semiconductor device, it is desired to reduce an area of the capacitor and film thickness of each constituent material. When the thickness of the dielectric film is reduced, intensity of an electric field generated by applying a constant voltage becomes greater, and hence a necessary voltage for operation of the device can be lowered. This also minimizes a surface step or step on a surface. The small surface step enhances fine work to be done above the step.
When the thickness of the dielectric film becomes equal to or less than 200 nanometers (nm), electric characteristics may be reduced in some cases. For example, there occur reduction of residual polarization charge and increase of leakage current. To produce a high-performance semiconductor device, it is desired to keep residual polarization charge at a high value and the leakage current at a low value.
In the process of crystallizing the dielectric material of oxide including lead, the element of lead is considered to contribute to formation of an initial kernel or nuclear in the crystallization. To achieve good crystallization, lead is favorably increased to an excessive extent. Excess lead causes increase of the leakage current after the crystallization. Therefore, a minimum quantity of excess lead for the crystallization is desired.
It is therefore an object of the present invention to provide a method of forming a dielectric film with high dielectric characteristics.
Another object of the present invention is to provide a method of forming a capacitor with high characteristics using a capacitor dielectric film including lead.
Still another object of the present invention is to provide a method of forming a semiconductor device with high characteristics using a capacitor dielectric film including lead.
According to one aspect of the present invention, there is provided a method of forming a dielectric film including the steps of forming on a surface of underlie substance a film of an oxide dielectric material including lead or bismuth, treating a surface of the oxide dielectric film with solution including nitric acid, and crystallizing the oxide dielectric film, after the surface treatment, by annealing the film and thereby obtaining an oxide dielectric film.
According to another aspect of the present invention, there is provided a method of forming a capacitor including the steps of forming on a surface of a first conductive layer a film of an oxide dielectric material including lead or bismuth, treating a surface of the oxide dielectric film with solution including nitric acid, crystallizing the oxide dielectric film, after the surface treatment, by annealing the film and thereby obtaining an oxide dielectric film, and forming a second conductive layer on said oxide dielectric film.
According to still another aspect of the present invention, there is provided a method of forming a semiconductor device including the steps of forming on a semiconductor substrate a transistor including one pair of current electrodes and a control electrode, covering the transistor with an inter-layer insulation film, forming a lower electrode on said inter-layer insulation film, forming on a surface of said lower electrode a film of an oxide dielectric material including lead or bismuth, treating a surface of the oxide dielectric film with solution including nitric acid, crystallizing the oxide dielectric film, after the surface treatment, by annealing the film and thereby obtaining an oxide dielectric film, and forming an upper electrode on said oxide dielectric film.
The obtained dielectric film has good crytallinity and a reduced surface layer.
Using the dielectric film, a capacitor with high electric characteristics can be fabricated.
Using the dielectric film, a semiconductor including capacitors with high electric characteristics can be produced. dr
The objects and features of the present invention will become more apparent from the consideration of the following detailed description taken in conjunction with the accompanying drawings in which:
FIGS. 1A to 1E are a flowchart and schematic cross-sectional views to explain processes of manufacturing an embodiment of a dielectric film and a capacitor according to the present invention;
FIGS. 2A to 2C are a graph and tables showing characteristics of samples in the embodiment according to the present invention;
FIGS. 3A and 3B are sketches of electro-microscopic pictures of samples produced by the embodiment;
FIGS. 4A and 4B are a flowchart of processes to fabricate a dielectric film and a capacitor and a sketch of an electro-microscopic picture of a sample in a prior art; and
FIG. 5 is a cross-sectional view schematically showing constitution of an embodiment of a semiconductor device according to the present invention.